Hydrolysis of wood with concentrated hydrochloric acid



Jan. 22, 1957 2,778,751

HYDROLYSIS 0F woon WITH CONCENTRATED HYDRO'CHLORIC ACID T. RIEHM Filed March 18, 1953 4 wgw Y ww hr1@ .Z f 9/ 4 fa fl United States Patent O nYDRoLYsIs oF woon WITH `colsrcEN'rR,Arno

HYDRoCHLoRIc ACID Theodor Riehm, Mannheim-Rheinau, Germany, assigner to Deutsche Bgin-Aktiengesellschaft, Mannheim- Rheinau, Germany Application March- 1-8, 1953, Serial No. 343,103 Claims priority, application Germany March 21, 1952 7` Claims. (Cl. 127'37) This invention relates, to, the hydrolysis of cellulosic materials with high concentrated' hydrochloric acid.

In the commercially used large scale saccharication of wood and similar materials, a battery of about 14 to 18 di'iusors is used which areV connectedr by a complicated system of pipes, for circulating and recycling the various solutions used and obtained in the process. The front diifusors are used for the sacchariiication proper and the' back ditusors serve for recovery of the hydrochloric acid from the. residual lignin. This, battery process is known as the fRheinau process; its. output isessentially governed by the charging sequence of' the diffusors which 'cannot be increased beyond about 5 hours per diffusor. Within thisl time interval, the foremost empty diffuser rnlist be charged with fresh wood in such a way that the Wood charged through a hooper provided at the top of the diffuser is continuously moistcned with a hydrochloric acid sugar solution. The hydrochloric acid sugar solution is then again Withdrawn from the bottom of the diffuser, passed through a cooler to carry away the reaction heat, and recycled to the hopper at the top of the diiusor. After the dilusor has been illed in this way with moistened `Wood, additional solution is charged andy the charge is allowed to stand for a 4certain time. Subsequently, the nished acid sugar solution ready for withdrawal is displaced from the newly mashed diffusor by the-eluent liquid of the succeeding diifusors. Afterwards, additional sugar -solution is swept out of this difiusr and employed for mashing and filling a fresh diffusor, Which has been emptied in the meantime. In this battery process, the wood -remains in the acid-for about 50 hours, if only the saacharication battery is considered, and for about 100 hours, ifv the Whole battery including the washing battery is considered.

It, has also been proposed to carry `out ther sacchariiication'in a continuous process in towers, `but such methods Could not yet be reduced to practice.

It is a principalrobject of the invention to provide a completely continuous sacchariiication process, which avoids. the ldrawbacks 'ofthe known methods and requires a relatively small reacting zone.

Another object of the invention is to provide a saccharication method, which does not require the use of mechanical elements.

'Still another object of the invention is to provide a sacchariication process in which the lignin can be washed without objectionable dilution. of the bulk of the hydrochloric acid.

In the conventional battery process about 21/2 times the amount of the theoretically required high concentrated hydrochloric acid must' be employed; because of the unavoidable dilution with water, more than half of this hydroehloric acid Vamount is withdrawn from the Washing battery in' the -form of an only medium concentrated hy- =drochloric acid, which has to be again enriched to the forigiual concentration, whereby the Water introduced into :the acid cycle must be sluiced out witha highconsump- 2,778,751 Patented Jan. 22, 1957 2 tion', of thermic energy. It is a further object of the invention to provide aprocess which needs only the theoretically required` amount of high concentrated hydrochloric acid.

It is still another object of the invention to provide an apparatus suitable for carrying out the new sacchariication process. p

According to the, invention, a liquid column consisting of defined contiguous zones is caused to travel continuouslythrough the stationary wood, and the Zones of the traveling column are maintained stationary by providing the reaction towers with inlets and outlets through which the required liquids are introduced into suitable zones of the traveling liquid column and through which suitable amounts of liquid are withdrawn from other zones, respectively.

l-norder to ensure an entirely uniform travel of the whole liquid column, wherein the concentration of the various Zones remains constant, theoretically an infinite or at least avery large number of inlet and outlets should be provided. l have found', however, that in practice a relatively small number of such inlets and outletsis sufficient. The intermittent advance of the aci-d flow is balanced by a layer of high concentrated substantially sugarfree hydrochloric acid between the acid sugar solution and the dilute acid, andl the` change of the direction of flow from the foremost to theA neXt succeeding tower is rendered innocuous by providing a sufliciently prolonged layer of a concentrated sugar solution containing, for instance, about 2() to 25 g. of sugar per 100 cml of solution.

The invention willbe explained more in detail with reference to the accompanying drawing, wherein Fig. l is a diagram illustratingthe successive operative stages in a saccharication apparatus according to the invention, land Fig. 2 is a dia'gramrnatigcalelevation of a tower which is conically tapered at top and bottom and suitable for use in the practice of the invention; the ligure illustrates the air andl water feed lines for removal of the residual lignin andthe draw-off lines for said lignin.

The keuaparatusconsists, for vinstan-ce, of 4 towers A, B, C, D, each con-taining 345 liters. The ratio of diameter to-height of the towers may be, for instance, 1:10. Each tower is provided at the top with an inlet and at the bottom with an outlet for the passage of the traveling liquid column, and additional uniformly spaced inlets or outlets are distributed overV the ylength of the towers. There may be, for instance, as shown in the drawings, two lateral inlets or outlets which divide the tower in three sections of substantially equal height. All the lines are provided with sieves. The towers are charged, for instance, each with about 81 kg. of prehydrolyzed dried beech wood. The liquid column, `divided into zones, flows in the direc tion of the arrows continuously through the towers.

Wood is charged continuously into the front tower A so as to vprovide at .all times for a wood layer above the liquid surface; the lheight of the wood layer must'be sucient to prevent escape of hydrochloric acid gas into the atmosphere.

The drawing illustrates the operations and the flow dia grams shortly before the end of each respective operation as follows:

Into the last tower D, wash Water is fed continuously through a in an amount of 33,8 1./h. until 0 hour. At the same time, dilute hydrochloric acid is continuously withdrawn through the lower lateral line at f. At the beginning, the concentration of said hydrochloric acid contains eventually only 0.5% of HCl. About 11.6 l./h.

'of dilute hydrochloric acid are drawn oli through f into the vessel F, and about 9.4 l./h. of about 41 percent hydrochloric acid are introduced over the same time into the top of tower C at b. From the bottom of tower C about 28.2 l./h. of solution pass continuously into the bottom section of tower B, while a corresponding volume of concentrated sugar solution liows from the top of tower B into the collecting tank E. ln this way, 61 l. of hydrochloric acid sugar solution have been withdrawn from tower B into the tank E until hour.

During the same time, a suitable quantity of wood has been charged into tower A at a uniform rate of about 6 kg/h. At 0 hour, the lines are switched in the manner shown in the drawing for hour. Otherwise, all the solutions and charges keep flowing continuously at the same rate. During this step, tower A is filled up to the level of the lower lateral line, whereupon again 61 l. of acid sugar solution are withdrawn therethrough into the collecting tank E. The drawing shows the apparatus at the end of this Step. At 5 hour, the lines are again switched, without any other changes in the feed and withdrawal of water, acid, sugar solution and wood, respectively. At 10 hour, tower D has been washed acidfree and is shut down. The wash water is lthen fed into the tower C. The shut down tower D is emptied and newly charged with wood, since in the meantime, tower `A has been filled up with dry wood. At hour, the wood layer in tower D has again reached a certain height.

In order to remove the lignin, water is injected into tower D from the bottom through a separate line p, and withdrawn at the top of the tower through a large stoneware Valve l and a pipe with about an 80 mm. diameter. The rate of flow of the water in the lower section of tower D is slowly increased to about 1.5 cm./sec., calculated on the free cross section of the tower. During this operation, theV lignin extends upwardly and partly liows out through the upper conduit. Subsequently, air is slowly added to the` aiuent water at the bottom of the tower until the ratio of water to air is about 1:1 by volume. ln this way, almost the entire lignin is swept out of the tower within a short time. Small amounts of larger lignin particles cannot be carried upwardly in this way without a substantial increase of the injected water and air amounts; they are drawn ott through a lower line n without, however, discontinuing the injection of water and air from the bottom before the tower has become free of lignin.

At 1500 hour, the apparatus is in the same state as at 000 hour, with the sole difference that the whole saccharilication column and the whole washing column have advanced by a full tower length. In the time from 150 hour to 2000 hour, the same operations take place as in the time between 000 hour and 500 hour.

The described process results in a complete saccharilication of the wood. No washing acid need be drawn olf, except the insignificant amounts (calculated as hydrogen chloride) in the form of very dilute hydrochloric acid, which can be used entirely for the prehydrolysis.

In the known battery process, the high heat of wetting had to be carried away by an uneconomic acid cycle through brine coolers; in the process of this invention, said heat remains as a very short heat wave always in front of the displaced sugar solution and is intermittently withdrawn from the apparatus together with said acid sugar solution. In the aforementioned example, only a few liters of the acid-sugar solution, when drawn oif through the respective outlets, are heated up to about 35 C., while the rest of said withdrawn acid-sugar solution and the entire other contents of the respective tower have a temperature not substantially exceeding 23 C. As the effluent acid-sugar solution is continuously vaporized immediately after withdrawal, any deterioration of the very heat-sensitive acid-sugar solution is automatically prevented in the new process. This is a great advantage over the battery process where, without the complicated cooli ing cycle, a whole ditusor volume would be subject to the' harmful effect of high .temperatures over a prolonged period of time.

The invention may be carried out with a smaller or larger number of towers, e. g. with 3 or 6 towers. I have, however, found that an apparatus comprising 4 towers oifers particular advantages for carrying out the invention on a technical scale. i

The reaction towers may be conically tapered at the top and bottom, as shown in Fig. 2. The ratio of diameter to height may be 1:4 to 1:10. According to the dimensions of the towers, particularly to their height, up to live or more equally spaced lateral inlets or outlets may be provided. In general, two lateral inlets or outlets have proved to be sufficient and satisfactory.

The invention is preferably carried out in such a way that a plurality of reaction towers is connected in series and that a continuous current of liquid is passed in each tower from the top to the bottom, whereby wash water is fed into the last tower D and about 41% HC1 preferably into about the middle of the series, for instance, into tower C; very diluted hydrochloric acid is drawn olf preferably from the last third of the series and hydrochloric acidsugar solution from the first tower A. The hydrochloric acid sugar solution, which may contain about 25 to 50 g. sugar per ccm. of solution, is withdrawn `in a volume corresponding to the sugar vconversion of the cellulose contained in the wood of one tower. The stronga ly diluted hydrochloric acid is drawn off in a volume which corresponds to the small amount of HCl, which has traveled towards the end of the tower series as a consequence of the continuous displacement of diffusion and mixing effects, so that a steep acid concentration gradient is maintained in the stationary state. Concentrated hydrochloric acid is admitted in a volume replacing the amount of HCl withdrawn in the hydrochloric acid sugar solution kand in the very diluted hydrochloric acid, yso as to maintain the hydrochloric acid content of the whole system. Wash water is added in such a volume that a tower newly charged with wood and connected to the series can be filled and the required volume of hydrochloric acid sugar solution can be drawn olf, taking into account the aforementioned added and withdrawn amounts of liquid.

The wood is charged into the front tower A continuously at such a rate that it forms above the liquid level a protecting layer of suicient height to prevent the breakthrough of hydrogen -chloride gas into the atmosphere. For removal ofk the heat of reaction, hydrochloric acid sugar solution is drawn off in `a ysuitable amount through each of the lateral pipes of the lforemost tower B which is being filled from the bottom with solution.

The process is carried out in such -a' way that there is maintained in the foremost part of the tower `system `a suiiicient zone ot' concentrated acid sugar solution, which extends over 1/2 to 1 tower length, subsequently a` sufficient saccharilication zone, then a short zone of substantially sugar free high concentrated hydrochloric acid, a subsequent washing zone of suicient length, characterized by Ia steep concentration decline, and a zone of substantially acid-free wash water, which zone intermittently lincreases to a full tower length and advances continuously through the whole wood column. This advance is brought about by effecting the feed and withdrawal of wash water `and hydrochloric acid at suitable places of the sacchan'- iication and washing system, by advancing in regular intervals the inlet of the acid and the youtlet of acid sugar solution by one tower section and the water inlet by 'a whole tower, yand by controlling the rate of ilow so that `the wood remains 8-30, preferably about l5 hours in the sacchariiication Zone.

ln 4 tower systems, the acid is introduced, preferably through Vtwo inlets, at a distance of l to 21/3 tower lengths, preferably 12/3 to 2 tower lengths, rearwardly of the liquid surface of the foremost tower; the diluted acid is drawn off at the distance of 1% to 2%, preferably 2`to 2% wird;

aaai-at tower length v wrdly of'said'liquidsurface,'i`.'e. Iabout 1/3-1/2 tower f'rarwadly `of theacid admission. Therwater feed isswitched from the top of the fourth tower at a-,to the top of the third tower at k when the first tower is filled4 to about two thirds, fso that there yis suiiicint time for emptying the last tower without interrupting the v'continuous charging of .the wood.l

In tht-:apparatus lshown in rl,v.each of :the four towers is provided with lateral branch pipes serving as inlets or outlets, which divide "theftower in 3 sections of aboutequal extension. E is ,the collecting vessel for the withdrawn sugar solution, and F is a collector for the strongly diluted hydrochloric acid obtained by the washing of the lignin, which acid is continuously withdrawn through a lateral outlet of the corresponding tower (f, g, h, respectively). The concentrated hydrochloric acid feed is advanced from b over c and d to e.

In Fig. 2 the devices m and l are valves for the circulation of sugar solution and Ihydrochloric acid.

What I 'claim is:

l. In the hydrolysis of wood with concentrated hydro chloric acid, the lsteps which 'comprise providing a plurality of separate stationary columns of lignin-containing prehydrolyzed cellulosic material, said columns being connected in series to form a saccharification unit, introducing continuously concentrated hydrochloric acid containing about 40% by weight of HC1 in to said unit to hydrolyze the cellulose to sugar, said concentrated hydrochloric acid forming in said unit a zone of fresh concentrated hydrochloric acid and in front thereof in the direction of flow a zone of acid sugar solution, intermittently withdrawing said acid sugar solution 'at a point'spaced by the length of at least one column from the point ot' admission of said concentrated hydrochloric acid, introducing continuously water into said lunit at a point rearwardly of the admission of said concentrated hydrochloric acid for removing hydrochloric acid from the. residual lignin, said water forming Va washing zone and in front thereof in the direction of ow a zone of dilute hydrochloric acid, intermittently advancing in the `direction of ow the admission of said concentrated hydrochloric acid `and said water and the withdrawal of said acid sugar solution, continuously withdrawing a portion of said dilute hydrochloric lacid at a point located between the points of admission of said water and of said `concentrated hydrochloric acid, and adjusting the admissions and withdrawals of the liquids so as to maintain o substantial equilibrium between the amounts of withdrawn and introduced HCl and a substantially uniform concentration in said zones during their advance through the unit.

2. ln the process as dened in claim l the step of introducing the concentrated hydrochloric acid in `an amount not substantially exceeding the theoretically required amount.

3. ln the process as defined in claim 1 the step of charging lignincontaining cellulosic material into the front column at a rate sufficient to maintain a laye-r of 'solid material above the surface of liquid, which layer prevents the escape of `hydrochloric acid gas into the atmosphere.

4. In the process as defined in claim 1 the step of injecting water into the bottom of a column of residual lignin freed from cellulose and hydrochloric acid so as to loosen said lignin, admixing air to said water, withdrawing said air and water carrying lignin suspended therein from the top of said column, and drawing off the portion of the lignin not suspended laterally from the bottom of the column.

5. In the hydrolysis of wood with concentrated hydrochloric acid, the steps which comprise providing separate successive batches of prehydrolized lignin-containing cellulosic material connected in series so as to form a saccharication unit having a first batch, a last batch, and at least one intermediate batch, directing a continuous liquid column through said unit in the direction from the last batch towards the front batch, introducing continuously concentrated hydrochloric acid containing about 40% by weight-of HC1 into fan-intermeuiafej-bfeii dfsia unit to vhydrolyz'ethe celluloseto sugar, said'concentr'ated hydrochloric acid forming in 'said unit azone df fresh concentrated hydrochloric acid andfin front thereof in the direction of lflow a zone of acid'y sugar solution, lintroducing continuously water vto the top of the last batch of -t-he unit for removing hydrochloric acid Yfrom "the residual lignin, said water forming "a washing 'zone ahd in front'thereof in the direction offlow a lzone of 'dilute hydrochloric acid, advancingthe introduction of water'to the next preceding batch after said zone 'of dilute hydrochloric acid has been displaced `from said last batch into the next preceding batch, intermittently advancing vin' the direction of iiow the admission of said concentrated hydrochloric acid, continuously withdrawing a portion of said dilute hydrochloric acid at a point located between the points of admission of said water and of said concentrated hydrochloric acid, intermittently advancing said point of withdrawal of dilute hydrochloric acid simultaneously and conforming with the advance of the point of admission of said concentrated hydrochloric acid, intermittently withdrawing acid sugar solution from the front of the liquid column adjusting the admissions and withdrawals of the liquids so as to maintain a substantial equilibrium between the amounts ofl withdrawn and in troduced HCl and a substantially uniform concentration in said zones during their advance through the unit, removing the last batch after the water introduction 'has been switched to the next preceding batch, providing a batch of fresh prehydrolyzed lignin-containing cellulosic material, making said batch the irst batch of said unit and continuing applying the recited sequence of steps to said unit, thereby removing said last batch and replacing said first batch whenever the water introduction has been switched from the last batch to the next preceding batch.

6. A continuous wood saccharification process with concentrated hydrochloric acid containing about 40% by weight of HC1 comprising the steps of providing always three complete stationary columns of prehydrolyzed wood while a fourth column of said wood is being built up, said four wood columns being connected in series as a saccharication unit terminating with said fourth column; continuously directing a liquid column through said unit in the direction of said fourth wood column, said liquid column comprising successively in the direction of flow a washing zone, a zone of dilute hydrochloric acid, a zone of said concentrated hydrochloric acid, and a zone of acid sugar solution, said zones constituting in said order about 20%, 20%, 10%, and 50% of the total length of said liquid column, respectively; intermittently withdrawing said acid sugar solution from the front end of the advancing 'liquid column at a point below the top of said fourth wood column; advancing at predetermined intervals said point of withdrawal conforming to the build up of said fourth wood column; continuously introducing said concentrated hydrochloric acid at a .point spaced by the length of about l to 21/3 wood columns rearwardly of the front end of said liquid column; continuously introducing water to the top of the wood column preceding in the direction -of flow of the liquid column that wood column which received the concentrated hydrochloric acid; intermittently advancing the admission of said concentrated hydrochloric acid conforming to the advance of the point of withdrawal of the acid sugar solution; continuously withdrawing a portion of dilute hydro-4 chloric acid at a point located between the points of admission of said water and of said concentrated hydro chloric acid, and advancing said point of withdrawal at predetermined intervals conforming to the advance of the point of introduction of said concentrated hydrochloric acid; adjusting the amount of introduced concentrated' hydrochloric acid so as to substantially replace the amount of HC1 withdrawn as sugar solution and dilute hydrochloric acid; intermittently removing the wood column which has been passed by said zone of dilute hydrowww chloric acid afterthebuild up of a fourth wood `column Iisbenfcombl'ted, replacing said exhausted 11i/oody col- `b`y"bui1dingup` afresh column of prehydr'olyzed Wood and making `said'fresh column, while beingbult up, the fourth column of said saccharication unit; and continuing the ow of said 4liquid column through said unit while said exhausted wood column is replaced by a column of fresh material.

7. Theisaccharication process as claimed in claim 6, wherein the points of withdrawal of sugar solution and the points of admission of the concentrated 'hydrochloric acid are advanced in intervals of about 5 hours by the length of about 1/3 of a wood column.

V References Cited in the le ofvthis patent Y, Y l

VUNITED STATES PATENTS l Hagglund Iune"30,f192`5 Aeree July 28, `1931 Scholler et a1 Feb. 5, 1935 Mohr Apr. 30, 1940 Boinot Aug. 24, 1944 Ant-W. Aug. 1, 1950 FOREIGN PATENTS Great Britain Apr. 4, 1949 

1. IN THE HYDROLYSIS OF WOOD WITH CONCENTRATED HYDROCHLORIC ACID, THE STEPS WHICH COMPRISE PROVIDING A PLURALITY OF SEPARATE STATIONARY COLUMS OF LIGNIN-CONTAINING PREHYDROLZED CELLULOSIC MATERIAL, SAID COLUMNS BEING CONNECTED IN SERIES TO FORM A SACCHARIFICATION UNIT, INTRODUCING CONTINUOUSLY CONCENTRATED HYDROCHLORIC ACID CONTAINING ABOUT 40% BY WEIGHT OF HCI IN SAID UNIT TO HYDROLYZE THE CELLULOSE TO SUGAR, SAID CONCENTRATED HYDROCHLORIC ACID FORMING IN SAID UNIT A ZONE OF FRESH CONCENTRATED HYDROCHLORIC ACID AND IN FRONT THEREOF IN THE DIRECTION OF FLOW A ZONE OF ACID SUGAR SOLUTION, INTERMITTENTLY WITHDRAWING SAID ACID SUGAR SOLUTION AT A POINT SPACED BY THE LENGTH OF AT LEAST ONE COLUMN FROM THJE POINT OF ADMISSION OF SAID CONCENTRATED HYDROCHLORIC ACID, INTRODUCING CONTINOUSLY WATER INTO SAID UNIT AT A POINT REARWARDLY OF THE ADMISSION OF SAID CONCENTRATED HYDROCLORIC ACID FOR REMOVING HYDROCLORIC ACID FROM THE RESIDUAL LIGNIN, SAID WATER FORMING A WASHING ZONE AND IN FRONT THEREOF IN THE DIRECTION OF FLOW A ZONE OF DILUTE HYDROCLORIC ACID, INTERMITTENTLY ADVANCING IN THE DIRECTION OF FLOW THE ADMISSION OF SAID CONCENTRATED HYDROCLORIC ACID AND SAID WATER AND THE WITHDRAWAL OF SAID ACID SUGAR SOLUTION, CONTINOUSLY WITHDRAWING A PORTION OF SAID DILUTE HYDROCHLORIC ACID AT A POINT LOCATED BETWEEN THE POINTS OF ADMISSION OF SAID WATER AND OF SAID CONCENTRATED HYDROCHLORIC ACID, AND ADJUSTING THE ADMISSIONS AND WITHDRAWALS OF THE LIQUID SO AS TO MAINTAIN A SUBSTANTIAL EQUILIBRIUM BETWEEN THE AMOUNTS OF WITHDRAWN AND INTRODUCED HC1 AND A SUBSTSNTISLLY UNIFORM CONCENTRATION IN SAID ZONES DURING THEIR ADVANCE THROUGH THE UNIT. 